Do you perceive any depth to the above image or do you see it all as relatively flat? Not everyone will see these images as dimensional (or even dimensional in the same way!)
One of the reasons that you might find the images rather dimensional is a fascinating perceptual phenomenon called Chromostereopsis.
Chromostereopsis is a phenomenon whereby the impression of depth is elicited from the juxtapositions of certain colors (most often with red-blue or red-green colors, but also occurring from red-grey or blue-grey images. This phenomenon, noted by Goethe in his 1810 book Theory of Colors, is generally attributed to some form of chromatic aberration.
There have been quite a few interesting hypotheses put forward to explain this colorful perception of depth. For a long time, many have thought that it was due to the way that the eye focused different wavelengths. Red (a longer wavelength) was thought to focus further back in the eye and blue (far shorter) further front, thus resulting in a perceptual disparity. Other gravitated to the work of Stiles and Crawford who in 1933, discovered that the light sensitivity differed for rays entering through center versus those entering from peripheral regions of the eye (thus leading to another potential perceptual disparity among certain juxtaposed wavelengths).
However, in more recent years, evidence seems to demonstrate that while all wavelengths of light are indeed focused onto the retina, shorter wavelengths tend to be focused more toward the nose while the longer ones are focused more toward the ear. This non-correspondence of retinal positions during binocular viewing can elicit an experience of depth, in which closer objects are focused more toward the ear and farther ones more toward the nose. However, this still does not explain reversal effects in which some people perceive blue as more distant than red.
So while there is indeed debate over the mechanisms—you might want to experiment with this yourself to see if you might open another channel to promote depth in your work.
For more information: http://luminanze.com/writings/chromostereopsis_in_ux_design.html
Additional examples: http://www.ritsumei.ac.jp/~akitaoka/scolor-e.html